Pink Was For Boys, Blue For Girls

“There has been a great diversity of opinion on the subject, but the
generally accepted rule is pink for the boy and blue for the girl. The
reason is that pink being a more decided and stronger color is more
suitable for the boy, while blue, which is more delicate and dainty, is
prettier for the girl.” Ladies Home Journal, June, 1918, on colourlovers, via kottke